2015 articles

The cauliflower mosaic virus promoter in GM crops: Should we worry?

The promoter turns up in the blood and brain of rats that eat GMOs – but while there’s no proof it does harm, there’s no proof it’s safe either

Recently GMWatch reported on a new study that showed that ingested fragments from the CaMV (cauliflower mosaic virus) promoter used in many GM crops incorporated into blood, liver, and brain tissues of experimental rats. Below are the aggregated comments of some scientists on the implications of this finding.

Scientists: The concern is not to do with the CaMV (cauliflower mosaic virus) promoter itself and what we know about its behaviour in its natural context. The concern is that this is a DNA sequence in a novel context, and we don’t know how it will behave in that new context. Even if the commercial versions of the CaMV promoter engineered into GM crops had an identical sequence to that of the natural virus, what it does in its new context (the GM plant) is not predictable.

What is known about the CaMV promoter is that it contributes to transcription initiation (the first step of gene expression) in the GM plant. But this occurs in the context of many other changes, possibly including those triggered by other DNA sequences which are inserted into the GM plant and which also contribute to transcription initiation in as yet unknown ways.

Surprisingly, these fragments of DNA are taken from parts of different genes and in their natural context they are not associated with transcription initiation! This, as much as any other evidence, shows that what a sequence is said to do in one context is not predictive of what it can do in another. So a potential unintended effect of the CaMV promoter in GM crops could be insertion and subsequent transcription of something that otherwise would not be transcribed. Alternatively it may have an affect that is not predictable from what we know about the natural functioning of similar-sequence DNA of virus origin.

Of course, all the above could be true of any dietary DNA. Nevertheless, that does not mean that these particular DNA sequences should not be tested for harm.

The key difference with the CaMV and other promoters is that they do not have a history of safe use in the way that they are being used in GM crops. In nature, the cauliflower mosaic virus infects brassica crops, such as cabbages. But even if there were no difference between the CaMV promoters in GM crops and the natural virus sequence, there is no proof that these natural virus sequences are in every cell of 100% of the brassicas we eat. They are almost certainly not present in any maize and soy that we eat. But the use of the CaMV promoter in all these species of GM crops means that it could be present in up to 100% of that material.

How these GM foods are prepared and where they are released in the body of the consumer at different stages of digestion may also affect the range of tissues exposed to the CaMV promoter.

The issue of dietary DNA may be more to do with principle than actual harm. For decades, some scientists and industries have denied, on the basis of no valid research, that dietary DNA could survive cooking and digestion. The fact that they have been proven wrong by this study and others before it raises questions about their credibility. But this fact alone is unlikely to trigger regulatory change unless it is coupled to a demonstration of harm.

The questions that should now be addressed are: • What are the novel potential expression products that result from the CaMV promoter and other DNA sequences inserted into GMOs? These may be novel RNA or proteins.• What do these expression products do, apart from what the genetic engineers intend them to do?

Answering these questions with actual data would enable this particular thread of the GMO safety debate to move beyond non-evidence-based claims of safety on one hand and speculation about possible harm from this promoter on the other.